CHAIN SKIPPING, or slipping of the chain while pedaling or shifting, is a common and annoying problem. Usually it happens while riding uphill, or under heavy pedal pressure, and results in fatique and loss of power - if not an outright accident!!
*Here are the top ten causes of CHAIN SKIP>>>>
Improper cable tension to the rear derailleur Fine tune the cable tension using the handlebar barrell adjusters so that the chain is centered on each cog on the rear cassette when it shifts
Worn or sticking cable This is a prime suspect in chain skip and often overlooked, so remove and lubricate your cable or replace it
Loose cassette Your rear cassette is loose on the hub and needs to be tightened
Worn, bent or broken teeth If your rear cogs are bent, worn, or missing teeth, this can cause shifting trouble - inspect, and repair or replace.
Dirty chain, kink in chain or rusty chain Your chain should be cleaned and lubed as one of the first attempts to correct a shifting problem - free any tight links, and scrub clean with a brush and then lube and remove excess
Damaged freehub body The freehub body coveys the energy from the cassette to the hub - it connects the two - and if it is starting to strip or is excessively worn, you will get lockup or chain skip
Debris in cogs Clean the rear cogs well and remove any debris or material that could be clogging them up
Bent derailleur cage or hanger Check the rear derailleur hanger and cage to see that it is not bent, and in the proper chainline
Loose hub If the rear hub is very loose, the bike might not shift properly - so check the hub for wobbling or side to side motion
Wheel not centered in dropout Make sure the rear wheel is centered in the rear frame dropouts before tighteneing the quick release or axle.
Chain length Your chain may be too long ot too short and cause shifting problems - also it may be excessively worn and require replacement.